1. Field of the Invention
The present invention relates generally to the packaging industry. In more specific aspects, the present invention relates to multiwall packaging and methods for forming multiwall packaging that have vents associated therewith.
2. Description of the Related Art
As more and more industrial, commercial, and consumer products are packaged, the need for enhanced end product packaging continues to grow. End product packaging not only has to keep the products fresh, the product packaging often needs to protect the environment from the product contents and protect the product contents from the environment. The packaging must also be strong enough to hold materials of varying weights, without being damaged, in order to provide packaging for a vast array of consumer products.
Of particular importance is often the ability to extract the contents of a package such as a bag without contaminating the contents with a contaminated outer surface of the bag. Various bags have been developed in attempts to satisfy this requirement. The typical bag includes integrated inner and outer plies, a flexible sheet material formed into a tubular form, and the tubular form being converted into an open mouth bag. At least one ply of the flexible sheet material for the bag can be coated with a moisture impervious plastic coating, laminated with a waterproof material, or be formed of a waterproof material. One such bag, for example, can be seen in U.S. Pat. No. 4,088,264 by Vogt titled “Multiwall Pouch Bags Or Detached Packaging Of Commodities.” The bag is formed by first heat sealing and severing an inner plastic tube from an outer paper tube to form a pouch of the inner tube. The inner tube is attached to the outer tube only at the open bag end. The outer plies are closed at a distance below the sack in a sewn or pinch bottom closure to close the bag at the closed end. After the bag is filled at the open end with a commodity to be packaged, the inner pouch into which the commodity is loaded is heat sealed to closure adjacent the open end and also severed from that end in a manner similar to severing the lower end of the inner pouch. As packaged, the commodity is contained within a sealed, sift and leak proof, inner pouch which is housed within a sealed outer tube for protection against environmental concerns such as contamination and insect penetration. A significant difficulty arises, however, when air is trapped in the inner pouch of the bag prior to sealing.
In such situations, it is important to permit air or gas release after the bag has been packed and the open end of the bag and the plastic pouch or poly liner have been sealed. It is also important to prevent contamination due to the venting of the trapped air. Applicants have recognized that when the plastic liner inside an unvented bag is sealed after being filled, it traps air and causes the bag to be difficult to handle and stack. The unvented bags essentially have a balloon affect after being sealed. There is also the risk that end seals in unvented bags will rupture during stacking processes due to excess pressure being applied. This problem is accentuated where the facility filling the bags is located at a different pressure altitude than a destination facility. Vents made by piercing a single ply plastic pouch or liner have been found to be ineffective as they allow material to sift out and insects to infest the material inside which often consists of food or pharmaceutical grade product. To allow venting of trapped air, others have developed various types of bags with various methodologies of venting.
Some of the first attempts included perforating the bag with very small holes in order to vent the trapped air. For example, U.S. Pat. No. 2,593,328 by Meaker titled “Perforated Multiple Ply Bag” describes a waterproof bag formed of electrically perforated paper. Each of the plies that form the body of the bag is electrically perforated to provide minute burrless perforations through which air trapped in the bag during filling may escape. The perforations are small enough to prevent the commodity with which the bag is filled from passing through the perforations or outside water from entering such perforations.
Another methodology includes using a single vent valve-type bag. For example, U.S. Pat. No. 3,958,749 by Linder et al. titled “Bacteria Proof Plastic Bag For Articles To Be Sterilized” describes a bag having a single valve which is gas and steam permeable at increased temperatures and which closes at a given normal temperature so that no bacteria can enter. The valve includes a filter device formed of a layer of water-soluble adhesive, a gas permeable layer, and a heat resistant adhesive having a plurality of holes. Also, U.S. Pat. No. 3,989,182 by Stearley titled “Vented Bag” describes a bag including a valve member which is positioned between one of the end flaps of the overlapped side flaps and a plurality of venting perforations formed in one of the end walls for providing venting of the interior of the bag to the atmosphere.
Yet another methodology developed has been the formulation of the bag using overlapping perforated margins from a continuous web of flexible plastic material. For example, U.S. Pat. No. 3,302,859 by Perry titled “Bag” describes a bag having a longitudinal seam including overlapping margins of plastic material from which a tube is formed. The margins are secured together using two spaced longitudinal seams of adhesive. Each margin has a series of tongues for the escape of air from the bag whereby the tongues in one margin are offset from the tongues in the other. U.S. Pat. No. 4,470,153 by Kenan titled “Multiwall Pouch Bags with Vent Strip” expanded on this design. The Kenan patent describes a bag having an interior plastic pouch formed from a sealed plastic tube having a longitudinal seam created by overlapping tube margins. The margins forming the longitudinal seam are secured together using two spaced-apart longitudinal seams of adhesive placed on opposite sides of a filter type spacer. The inner margin has a series of holes that allow air to escape from inside the interior plastic pouch into a channel formed between the inner and outer margins. Air escapes from the channel either through a set of holes in the outer margin or through a heat seal closure. Also, U.S. Pat. No. 4,550,441 by Keppel titled “Vented Bag” further developed this methodology. The Keppel patent describes a multiwall commodity bag as an improvement upon U.S. Pat. No. 4,470,153 by Kenan where in lieu of a series of vent holes or openings along one or both of the overlapped margins of the channel, a small hole the size of a pinhole is formed through the inner side of the center of the overlap forming the channel near one end. A small hole is also formed through the outer side and near the center of the channel adjacent the other or opposite end of the plastic pouch. Applicants have recognized that these type of seamed bags, however, can have problems with seam overlap alignment and can be complex to manufacture.
Also, bags have been developed that attempt not only allow the protection of the contents from contamination yet are capable of releasing trapped air, and allow for the extraction of the contents without contaminating the contents with a contaminated outer surface of the bag, but bags that are also easy to load, stack, and palletize. These bags are typically formed using a pinch bottom whereby the commodity-holding pouch is formed from an inner plastic ply that is heat sealed at the pinch closure of the outer enclosing bag and open at the opposite end for receipt of a product to be packaged. Upon filling the bag to the desired amount, the inner plastic ply is heat sealed to close the open end and may remain attached or optionally be severed from the top end of the outer plies using a pair of beveled compression rollers. Applicants have recognized that additional problems can be encountered with this type of bag arrangement, however. For example, often the unfilled inner plastic bag in the standing position is much shorter in length than the enclosing outer paper bag. This can cause uneven or excessive pressures on the lower plastic seal creating a potential for seal failure or pinholing. Some attempts to solve this problem were made as seen in U.S. Pat. No. 5,281,027 by Thrall titled “Multiple Ply Bag with Detachable Inner Sealed Pouch for Packaging Products” which describes using a seamless inner heat sealable ply that is as long as the outer paper bag during the filling process and that is freely folded and fully detachable in a non-adhesive manner at the bottom end of the pinch bottom bag. Additionally, U.S. Pat. No. 5,553,943 by Cook et al. titled “Multiple Ply Plastic Line Bag with Satchel Bottom” describes using a seamless inner plastic pouch capable of heat sealing wherein the plastic pouch is foldably, non-adhesively and detachably arranged at the satchel bottom of the bag. The satchel bottom is formed by slitting, folding, and overlapping stepped paper plies adhesively bonded to form the satchel bottom and to loosely retain the pouch independently and away from the adhesive bond. Applicants have recognized that there is still a need, however, for alternative type vented bags and packaging that addresses problems associated with products sifting and insect infestation and yet is easy and cost effective to manufacture.